Variable mechanical valve timing mechanism having an adjusting device

ABSTRACT

A variable mechanical valve timing mechanism for adjusting the stroke of gas exchange valves in a reciprocating-piston internal combustion engine, having a plurality of cams ( 5 ) which are fastened to a camshaft ( 4 ), having a plurality of gas exchange valves ( 1 ) and valve actuating elements ( 2 ), having adjusting units which have a plurality of adjusting elements ( 7 ) which are fastened to at least one rotatable adjusting shaft ( 6 ), having transmission apparatuses which comprise transmission elements ( 8 ), the transmission elements ( 8 ) being operatively connected to the cams ( 5 ), to the valve actuating elements ( 2 ) and to the adjusting elements ( 7 ) directly or with the interconnection of transmission members (adjusting rollers, cam rollers), and having at least one adjusting device on the rotatable adjusting shaft ( 6 ), the adjusting shaft/shafts ( 6 ) and adjusting elements ( 7 ) being configured and arranged in such a way and/or the number and position of the adjusting devices (adjusting levers  10 ) being selected in such a way that all of the gas exchange valves ( 1 ) have substantially the same stroke adjustment in relation to one another.

FIELD OF THE INVENTION

Variable mechanical valve timing mechanism for adjusting the stroke ofgas exchange valves in a reciprocating-piston internal combustionengine, having a plurality of cam which are fastened to a camshaft,having a plurality of gas exchange valves and valve actuating elements,having adjusting units which have a plurality of adjusting elementswhich are fastened to at least one rotatable adjusting shaft, havingtransmission apparatuses which comprise transmission elements, thetransmission elements being operatively connected to the cams, to thevalve actuating elements and to the adjusting elements directly or withthe interconnection of transmission members (adjusting rollers, camrollers), and having at least one adjusting device on the rotatableadjusting shaft.

BACKGROUND OF THE INVENTION

Variable mechanical valve timing mechanisms of this type for adjustingthe stroke of gas exchange valves in a reciprocating-piston internalcombustion engine are known from DE 100 06 016 A1 and DE 100 06 018 A1.

Although these valve timing mechanisms differ in terms of thetransmission elements between the cams of the camshaft, the valveactuating elements and the adjusting elements, a common feature oftheirs is that the individual adjusting elements have curved paths onwhich the transmission elements slide or roll. Depending on the positionof the rotatable adjusting shaft and thus of the curved paths of theadjusting elements, the valve actuating elements and thus the gasexchange valves are moved to a greater or lesser extent, with the resultthat the stroke of the gas exchange valves is adjusted, in particularthe stroke of the inlet valves of the reciprocating-piston internalcombustion engine. Depending on the stroke adjustment, considerableforces occur at the adjusting elements, which forces lead to torsionalloading of the adjusting shaft, with the result that, depending on thespacing between the adjusting elements and the adjusting device, thestroke is adjusted incorrectly, in the, sense that the gas exchangevalves are not opened sufficiently or completely. Depending on thenumber of cylinders of the reciprocating-piston internal combustionengine and the therefore necessary length of the adjusting shaft, inconjunction with the point of action of the adjusting device, this canlead to substantial deviations in the valve stroke.

OBJECT OF THE INVENTION

It is therefore an object of the invention to improve a variablemechanical valve timing mechanism of the generic type having anadjusting device, in such a way that the deviations in the valve-strokeadjustment are eliminated or reduced to such a large extent that asubstantially uniform cylinder filling and smooth running of theinternal combustion engine are ensured.

SUMMARY OF THE INVENTION

The object of the invention is achieved in that the adjustingshaft/shafts and adjusting elements are configured and arranged in sucha way and/or the number and position of the adjusting devices areselected in such a way that all of the gas exchange valves havesubstantially the same stroke adjustment in relation to one another.

This is initially possible as a result of the fact that the adjustingshaft/shafts is/are adapted to the torque loading accordingly bysuitable selection of the section moduli of the loading, and/or as aresult of the fact that the adjusting elements or their curved paths andangular positions on the adjusting shaft are selected in such a way thatidentical stroke adjustment takes place substantially. However, it isalso possible to select the number and position of the adjusting devicesin such a way that the spacing between the adjusting elements and theadjusting devices is reduced.

In one advantageous refinement of the invention, it is proposed that aplurality of adjusting devices are provided along an adjusting shaft,preferably uniformly distributed. As a result, the spacing between therespective adjusting device and the adjusting elements is shortened,with the result that the rotational angle of the adjusting elements withrespect to the adjusting device is reduced accordingly.

In one preferred refinement of the invention, it is proposed that theadjusting shaft is subdivided into a plurality of sectional shafts, andeach sectional shaft is assigned an adjusting device. Thus, for example,in a valve timing mechanism for a four-cylinder reciprocating-pistonengine, the adjusting shaft can be divided into two sectional shaftswhich each have an adjusting device, with the result that, depending onthe number of inlet valves per cylinder, one or two adjusting elementswhich are at a small distance from the adjusting device are arranged ineach case on each side next to the adjusting device.

In a six-cylinder engine, for example, three sectional shafts havingthree adjusting devices for in each case two cylinders can be used, orelse one or two sectional shafts having two adjusting devices for ineach case three cylinders.

In the extreme case, each cylinder can be assigned one sectional shafthaving an adjusting device. However, this then leads to costs whichcannot be ignored, with the result that it is necessary to perform acost/use analysis with regard to the number of sectional shafts havingadjusting devices.

In an advantageous manner, the adjusting device is arranged centrally onthe adjusting shaft or the sectional shaft or, in the case of aplurality of adjusting devices, it is to be arranged on an adjustingshaft in such a way that the load distribution is symmetrical.

The adjusting device can be of any desired configuration. An electric,hydraulic or mechanical actuator can be provided which interacts withtoggle levers, gearwheels, worm gears and spindles or hydrauliccylinders

However, it is significant that the actuators or the adjusting devicesare activated synchronously and with identical adjusting variables, withthe result that the adjustment is identical for all the gas exchangevalves.

In a further refinement of the invention, it is proposed that, startingfrom the adjusting device or devices, the section modulus is variedalong the adjusting shaft or shafts or sectional shafts in such a waythat all the adjusting devices have substantially the same adjustingangle. This can be achieved firstly in that the diameter is varied inaccordance with the spacing between the adjusting elements and theadjusting devise, in order to increase the section modulus accordingly.Secondly, depending on the configuration of the adjusting shaft or thesectional shaft, if it is constructed, for example, from parts, thesection modulus can likewise be adapted by suitable selection andvariation of the materials.

However, it is also possible for the adjusting cams of the adjustingelements and/or the angular position of the adjusting elements on theadjusting shaft or shafts or sectional shafts to be modified in order toattain an identical stroke adjustment of the gas exchange valves. Theconcept of the invention can namely also be realized in that, takinginto consideration the rotation of the adjusting shaft, the adjustingelements are mounted at the respective location in a leading angularposition, with the result that the stroke adjustment is correctedaccordingly. For this purpose, it can be necessary to adapt the curvedprofile accordingly, as the adjustment would be excessively pronouncedin the event of relatively small stroke adjustment and thus relativelylow forces on the adjusting elements or relatively low torque on theadjusting shaft.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to explain the invention further, reference is made to thedrawings, in which exemplary embodiments of the invention are shown insimplified form, and in which:

FIG. 1 shows a perspective view of a variable mechanical valve timingmechanism having a rotatable adjusting shaft,

FIG. 2 shows a side view of the valve timing mechanism according to FIG.1, as seen in the direction of the adjusting shaft,

FIG. 3 shows a side view of the valve timing mechanism according to FIG.1,

FIG. 4 shows a perspective view of a variable mechanical valve timingmechanism having two rotatable adjusting shafts,

FIG. 5 shows a side view of the valve timing mechanism according to FIG.4, as seen in the direction of the adjusting shaft, and

FIG. 6 shows a side view of the valve timing mechanism according to FIG.4.

DETAILED DESCRIPTION OF THE DRAWINGS

In FIGS. 1 to 6, unless shown in detail, gas exchange valves are denotedby 1, which gas exchange valves are installed in the cylinder head of areciprocating-piston internal combustion engine. The gas exchange valvesare inlet valves which control the inlet flow of air or an air/fuelmixture. The reciprocating-piston internal combustion engine shown is anengine with a row of four cylinders which each have two inlet valves.Each gas exchange valve 1 is operatively connected to a valve actuatingelement 2 which is configured as a drag lever which is supported on ahydraulic tappet at that end which faces away from the gas exchangevalve 1.

Furthermore, 4 denotes a camshaft which is mounted in the cylinder headof the internal combustion engine and to which cams 5 are fastened. Anadjusting shaft 6 is arranged parallel to the camshaft 4, whichadjusting shaft 6 (likewise in a manner not shown) is mounted rotatablyin the cylinder head of the internal combustion engine. Adjustingelements 7 are arranged fixedly on the adjusting shaft 6 so as to rotatewith it, each gas exchange valve 1 or each valve element 2 beingassigned an adjusting element 7.

Furthermore, transmission elements 8 are arranged between the cams 5 ofthe camshaft 4, the adjusting shaft 6, the adjusting elements 7 and thevalve actuating elements 2, which transmission elements 8 have a rockerarm which is actuated by the cams 5, is supported on the adjusting shaft6 and displaces guide members which roll on an adjusting cam 9 of theadjusting elements 7; in the process, the valve actuating element 2 ispivoted and the gas exchange valve 1 is opened. The stroke of the gasexchange valves is adjusted from a zero or minimum adjustment to themaximum stroke adjustment as a function of the rotational position ofthe adjusting shaft 6 and thus of the adjusting elements 7 and theadjusting cam 9. A spring element 11 which ensures restoring of therocker arms and thus contact of the rocker arms with the cams 5 is inoperative contact with each end of the rocker arms which faces away fromthe cams 5.

An adjusting device which can have various configurations, as explainedin the general description, is operatively connected to the adjustingshaft 6. For the sake of simplicity, it is configured as an adjustinglever 10 in FIGS. 1 to 6.

As can be seen easily, large forces are produced on the adjustingelements 7 and adjusting shaft 6 as a result of the high rotationalspeed of the camshaft 4 and the large accelerations of the cams 5 ontothe transmission elements, as the transmission elements also come intocontact with the adjusting cam 9 with high acceleration. If only oneadjusting unit or one adjusting lever 10 is then attached at the end orin the middle of an adjusting shaft 6 for a four-cylinder engine or evena six-cylinder engine, high rotational deformations occur in theadjusting shaft 6, which lead to incorrect stroke adjustment of the gasexchange valves 1.

If, therefore, according to the invention, in each case one adjustingdevice or one adjusting lever 10 is attached between the cylinders 1 and2 and the cylinders 3 and 4 in a four-cylinder engine, the rotationalangle of the adjusting elements 7 is reduced considerably in relation tothe adjusting lever 10, on account of the shortening of the path.

In FIGS. 4 to 6, the adjusting shaft 6 is divided into two sectionalshafts 12, and each sectional shaft 12 is assigned an adjusting device,distinguished by the adjusting lever 10, with the result that eachsectional shaft 12 is adjusted appropriately, without the adjustingdevices being influenced relative to one another.

Both in the exemplary embodiment according to FIGS. 1 to 3 and alsoaccording to FIGS. 4 to 6, it mast of course be ensured that theadjusting devices rotate the adjusting shafts 6 or the sectional shafts12 at the same adjusting angle and synchronously, in order that thestroke of all the gas exchange valves 1 is adjusted uniformly.

The optimum case for the stroke adjustment accuracy and naturally alsofor the costs would exist if each cylinder were assigned a dedicatedsectional shaft with dedicated adjusting unit (adjusting lever 10).However, this would also lead to high costs. For this reason, acompromise between adjusting accuracy and costs has to be made.

As defined in the general description and the patent claims, the sectionmodulus of the adjusting shaft or of the sectional shafts can be adaptedappropriately to the forces which act on the adjusting elements bydifferent material selection or by different diameters of the adjustingshaft or of the sectional shafts.

List of Reference Numerals

-   1 Gas exchange valve-   2 Valve actuating element-   3 Hydraulic tappet-   4 Camshaft-   5 Cam-   6 Adjusting shaft-   7 Adjusting element-   8 Transmission elements-   9 Adjusting cam-   10 Adjusting lever-   11 Spring element-   12 Sectional shaft

1. A variable mechanical valve timing mechanism for adjusting the strokeof gas exchange valves in a reciprocating-piston internal combustionengine, having a plurality of cams (5) which are fastened to a camshaft(4), having a plurality of gas exchange valves (1) and valve actuatingelements (2), having adjusting units which have a plurality of adjustingelements (7) which are fastened to at least one rotatable adjustingshaft (6), having transmission apparatuses which comprise transmissionelements (8), the transmission elements (8) being operatively connectedto the cams (5), to the valve actuating elements (2) and to theadjusting elements (7) directly or with the interconnection oftransmission members (adjusting rollers, cam rollers), and having atleast one adjusting device on the rotatable adjusting shaft (6),characterized in that the adjusting shaft/shafts (6) and adjustingelements (7) are configured and arranged in such a way and/or the numberand position of the adjusting devices (adjusting levers 10) are selectedin such a way that all of the gas exchange valves (1) have substantiallythe same stroke adjustment in relation to one another.
 2. A variablemechanical valve timing mechanism of claim 1, wherein a plurality ofadjusting devices (adjusting levers 10) are provided along an adjustingshaft (6), preferably uniformly distributed.
 3. A variable mechanicalvalve timing mechanism of claim 1, wherein the adjusting shaft (6) issubdivided into a plurality of sectional shafts (12), and each sectionalshaft (12) is assigned an adjusting device (adjusting lever 10).
 4. Avariable mechanical valve timing mechanism of claim 1, wherein theadjusting device (adjusting lever 10) is arranged centrally on theadjusting shaft (6) or the sectional shafts (12).
 5. A variablemechanical valve timing mechanism of claim 1, wherein, starting from theadjusting device or devices (adjusting lever 10), the section modulus isvaried along the adjusting shaft (6) or sectional shafts (12) in such away that all the adjusting elements (7) have substantially the sameadjusting angle.
 6. A variable mechanical valve timing mechanism ofclaim 1, wherein the adjusting cams (9) of the adjusting elements (7)and/or the angular positions of the adjusting elements (7) on theadjusting shaft (6) or sectional shafts (12) are modified in order toattain an identical stroke adjustment of the gas exchange valves (1) inrelation to one another.